1. Field of the Invention
The invention generally relates to holding a desired tension in a length of thread (yarn, wire, etc.) during interlacing with other threads. The invention is more specifically related to the application of different tensions between threads and variable lengths of time for holding the tension.
In particular, it concerns an apparatus for use with an interlacing apparatus, for example, a weaving loom, which is positioned just outside of the fabric selvage to control the tension of an inserted thread as it is stretched across the weaving loom thru an open shed.
2. Prior Art
It has been known that tensioning devices are desirable to control the threads and apply a predetermined tension to the thread during a certain time frame which is related to thread insertion. It is important to insert the thread with a specific tension to avoid slack or tight threads which diminish the product's quality. If the tension is too low, thread loops protrude from the fabric surface, or if the tension is too high, the fabric edges are pulled toward the fabric's center.
U.S. Pat. No. 4,976,292 describes a tensioning device that grips and holds the free end of an inserted thread while applying tension in synchronism with the insertion motion. The synchronized motion is achieved by the free end of the thread being pushed into the holding device during a beat-up motion.
In U.S. Pat. No. 5,105,856, the tensioning device is based on the concept that a thread guide pin, driven up and down in synchronism with the beat-up motion stretches, tensions the thread, either due to the return motion of the beat-up or by an additional component.
In U.S. Pat. No. 4,513,792, the tensioning device has a rod which oscillates at the cadence of the weaving machine transversely of the inserted thread position. The rod deflects the thread to a retaining element that holds it during the rod's upward movement. This device requires elaborate, synchronized control of the tensioner's movement.
In U.S. Pat. Nos. 5,462,094 and 5,725,029, the disclosed devices use brakes to control the thread's tension. Such brakes may control the tension during the process where a thread is paid out in a weaving loom. Such brakes may also be combined with sensors to stop the machine motion if the tension is too low or too high during the thread laying out process. Such brake systems may control different tensions as when multiple threads are inserted.